This invention relates to the production of cross sectional views of a body using ionizing radiation in general and more particularly to an improved method and apparatus for producing such a view.
Devices of this general nature in which radiation is directed through a cross-sectional plane of a body in different directions and the amount of radiation passing through the body converted into electrical signals and evaluated in an electrical storage system are known. Arrangements for carrying out such a method in which such a body is scanned by means of parallel displacement of the radiation source and the radiation receiver in the cross-sectional plane of the body are generally known as scanners.
In one known method of this type an X-ray or gamma ray source furnishes a beam of approximately parallel rays which are directed to penetrate the body to be examined in the desired cross-sectional plane. The radiation is absorbed by the body to a certain extent. The remaining radiation passes through the body. Behind the body to be examined a picture carrier is placed which the radiation strikes. Through a stepwise parallel displacement of the radiation source and picture carrier, the body elements in the cross-sectional plane are sequentially scanned. Subsequently, the radiation source and picture carrier are tilted at a predetermined angle with respect to an axis perpendicular to the cross-sectional plane and the cross-sectional plane of the body is again projected on the picture carrier by parallel displacement of the radiation source. In this manner the radiation source goes through the individual body elements in a different direction. By repeating this process several times each body element in the cross-sectional plane is imaged as often as the system is tilted about the axis. The conversion of these different individual exposures of the body elements and the correlation with the corresponding picture elements of the body cross-sectional view to be produced are obtained using an electronic computer into which are then entered, for example, 28,000 equations with 6,440 variables.
In one particular embodiment for an arrangement for carrying out such a method, the fan shaped radiation of a radiation source is subdivided using separate collimators into individual beams lying in the cross-sectional plane. By doing this the time required to obtain a sectional view is shorted. Behind the body a group of photodetectors are located with which a common reference scintillator having a light tube is associated. The output signals of these photodetectors or photomultipliers are further processed in electronic circuitry and then control a printer which furnishes a sectional view of the body. Such as disclosed in German Offenlegungsschrift No. 1,941,433. In this arrangement there is a stationary source for this scanning. The spaces between the individual photodetectors with the associated collimators are covered by an appropriate movement of the photo detectors.
Although this method and apparatus for producing such views is satisfactory it suffers from a number of disadvantages. In the first instance it takes too long. Some portions of the human body are always in motion and the previous method does not permit producing accurate pictures of those parts. Furthermore, the prior method suffered from a lack of resolution. To obtain good resolution with this prior arrangement an excessive equipment cost is required. A further serious disadvantage of the method was the amount of total radiation received by a human body being examined. Since a number of exposures were made the body was exposed to the radiation each time. Although it would be possible to increase the number of detectors in these prior art arrangements while decreasing their receiving area at the same time, this would require a corresponding increase in the power of the radiation source in order to obtain useful signals with an adequate signal to noise ratio, since, with the prior art photodetectors, relatively small signal to noise ratios are available. Very likely the radiation would have to be increased to an amount above that to which the human body should be exposed.
In view of these difficulties, the need for an improved system which can operate quickly, give good resolution and not subject the human body to large radiation doses becomes evident.